Induction motor



Dec. 18, 1928.

' 1,695,946 5. R. BERGMAN INDUCTION MOTOR Filed Nov. 29, 1924 4 F'Lgl. 1

Inventor Sven R. Bergman HLs Attornz'gy Patented Dec. 18, 1928.

UNITED STATES SVEN 3. 3mm, 01' HAEANT, MASSACHUSETTS, ABSIGNUR T GENERAL ELEUIRIC OOIPANY, A. CORPORATION OF NEW YORK.

INDUCTION MOTOR. I

Application filed November 29, 1924. Serial No. 752,988.

My invention relates to induction motors 1 is the magnetic core of an induction motor and particularly to squirrel cage rotors of such motors.

It ,is well known-that-in order that an induction motor should start under load without an execessive current flow, it is necessary that the secondary circuit shall possess a high resistance, and on the other hand, that when the motor is up to speed the resistance and the reactance of the secondary circuit should be low in order to secure etiicient operation.

It has been proposed heretofore to provide the secondary member of an induction motor with two squirrel cage windings, one of high resistance and low reactance and the other of low resistance and high reactance.- When starting with such an arrangement, the freuency of the secondary currents is high and t e high resistance winding will carry the greater part of the load, but when the motor 18 up to speed, the frequency of the secondary currents is low and the low resistance -low current consumption, and whic winding will carry the load.

M invention relates toinduction motors of the above described type, and has for its object, a novel construction of such a motor, which may be started by throwing the motor directly on the line without the use of a starting compensator, and when so started, will have afhigh starting to ue and may have at full load an efliciency as high and a very sli htly lower power factor than a standard induction motor provided with a sin le squirrel cge winding.

9 various atures of novelty which characterize my invention are pointed out with articularity in the claims annexed to and orming a part of this specification.

Fora better understanding of-my invention,

' reference maybe had to'the following description taken in connection with thesecompanying drawing, in which Fi 1 is a veiw partly in section of a mold an a rotor, the rotor representing its condition as it is read art y in section of my completed rotor and i 3 is an end view of the rotor of Fig. 2. he method of forming thesquirrel ca winding hereinafter set forth forms t e sub'ect matter of a divisional application,

Serial No. 257,203, filed February 27, 1928. It may be formed, however, in any well known manner. Referring to the drawing,

- narrow to leave the mold; Fig. 2 is a viewings of the inner row being connected with alternate openings of the outer row by lon ortions. Conductors substantialFy fill allo these openings. End rin 18 of small cross-section, integral with t e conductors in the outer row. of openings, form with these conductors a hi h resistance, low

.reactance winding, and en rings 19 of large cross-section, integral with the conductors in the inner row of openings, form with these conductors a low resistance, high reactance squirrel cage winding. In order to cast squirrel cage windings in the conductor receiving openings 2 and 3, the'core 1 is placed in a suitable mold formed in such amanner that the vslots will be entirely filled with conductor portions united at each end by a single end ring. I then, by a suitable tool, separate the single end ring into two portions in the bottoms of the deep slots. In the casting operation I preferably employ a mold com rising end flange portions 4 and 5 and a cy indrical portion 6. .The cylindrical portion 6 embraces the outer periphery of t e core member and the flange portions 4 and 5 are fastened together as by bolts 7 so as to firmly clamp together the laminations forming the core 1. These flange portions engage the laminations at their outer periphery and each is cut away so as to have formed therein two cylindrical grooves 8 and 9. The groove 8 is narrow, whereas the groove 9 is wide, for a purpose which will be hereinafter explained. The flange 4 has an opening 10 therein through which molten metal may be poured to form conductors in the conductor receiving openings 2 and 8 and end rings in the grooves 8 and 9 integral with thenonductors.

Thesquirrel cage windings may be cast sistance connecting together the conductor by any suitable method. I have chosen to illustrate the centrifugal method of the Reist and Maxwell Patent No. 1,190,009, dated July 4, 1916. The mold and core are rotated as a unit in any suitable manner. For this purpose, there is shown a mandrel 11 fastened in the shaft receiving opening 12 of the core 1, the mandrel having mounted thereon a pulley 13, the whole being rotated by means of a belt 14. While the core and mold are being rotated, metal is poured through the opening 10. This metal flows down the large portions 15 of the deep conductor receiving openings 2 and also partially down the shallow conductor receiving openings 3 and partially down the small portion 16 of the deep conductor receiving openings 2. Such metal after flowing down through the portions 15 of the openings 2 also flow up the openings 3 and the portions 16 of the openings 2 uniting with the metal which flows down these openings. Molten metal also fills the cylindrical grooves 8 and 9 forming end rings of large cross section, one at each end of the rotor core. Metal also flows into the intermediate long, narrow portions 17 of the deep conductor receiving openings, which units the conductors in the portions 15 and 16 of these openings into a single conductor. Suflicient metal is poured into the mold to form conductors in the slots 2 and 3 and end rings in the grooves 8 and 9. Rotation of the mold and core is continued until the molten metal has congealed. lVhen the mold and parts are sufciently cool to handle, the bolts 7 are removed, thereby permitting the parts 4, 5 and 6 of the mold to be removed. The conductors with their integral end rin firmly clamp the laminations together. fter the rotor is removed from the mold, the'end rings which were formed in the grooves 8 are machined in any suitable machine tool, so as to separate eachot thelarge end rings into two separ ate,'-con'centric end rings 18 and 19. The end rings 18 thus formed are of small cross-section and are integrally connected to the conductors formed in the shallow conductor receiving openings 3 and the conductors formed in the portions 16 of the deep conductor receiving openings 2 and form with these conductors a high resistance, low reactance squirrel cage winding. The end rings 19 are of large cross-section and are integrally connected with the conductors formed in the portions 16 of the deep conductor receiving openings 2 and form there with a low resistance, high reactance squirrel cage winding. I

I have shown the cylindrical grooves 9 of the flange portions of the mold provided with rectangular projections which act as cores to form longitudinally extending spaces 20 in the end rings 19. These spaces form. fan blades 21 on these end rings. If

desired, these projections may be omitted from the mold and the metal of the end rings machined away to form fan blades after the squirrel cages have been cast, or if desired, the fan blades may be omitted entirely.

In order to make a double squirrel cage motor, which can be thrown directly on a source of power and which will start under load with a small current consumption, it is necessary that the low reactance winding be of high resistance. I have found, however, that the smallest diameter of conductor receiving opening into which metal will flow and form a continuous conductor therethrough is about 2/ 10" of an inch. A squirrel cage winding formed of conductors of this size with end rings of large cross section united to both squirrel cages, is of too low a resistance to effect successful starting under the above conditions. I conceived the idea of placing a considerable portion of the resistance of the low reactance squirrel cage winding in the end rings thereof, making it possible to use sufiicient large slots for the conductors of this winding, so that it could readily be cast. In order to get the resist-- ance'of this end ring sufliciently high for this purpose, I form it as explained above. that is, by casting it integral with the end ring for the low resistance winding and then separating it therefrom by a machining operation.

The deep conductor receiving openings 2, as explained above, have a large portion 15 at the bottom thereof and a small portion 16 atthe top thereof, joined by an intermediate long, narrow portion 17. When the squirrel cage windings are cast, the conductors substantially completely fill these openings 2. The squirrel cage windings formed with the conductors in the small portion 16 of the slots is of high resistance for the reason pointed out above. It is of low reactance, because flux will not pass above it since the thin sections of the core above the openings 2 and 3 become saturated and, electrically speaking, the openings communicate with the periphery. On the other hand, the winding formed of the conductors in the larger portion 15 of the slots is of low resistance since not only are the conductors of large cross section, but so are the end rings joining them. This winding is of high reactance because of the narrow air gap provided above it by the long, narrow ortion 17 or the slots, across which flux Wlll pass when the motor is starting with little or no flux passing under this winding. I have found that the resistance of the low reactance winding should preferably be three times that of the higher reaotance winding, so that when the motor is operating at normal speed and under load, this high resistance winding will carry the maximum current consistent with good efficiency, obtaining at the same time the best possible power factor. The conductors in the portions 17 0f the slots have an intermediate value of reactance. The end rings 18 connect together the conductors 16 having relative low reactance and the conductors 17 having an intermediate value of reactance, and the end rings 19 connect together the conductors 15 having a relatively high reactance.

The squirrel cage windings are preferably cast out of aluminum, but any other suitable metal may be used. If desired, the shallow conductor receiving openings 3 may be omitted, and the high resistance winding all placed in the portions 16 of the slots 2, and I aim in the appended claims to cover such a modification of my invention as well as an others which do not depart from the spirit and-scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is 1. In an induction motor, a. rotor having two concentric rows of conductor receiving openings, adjacent openings of the inner row being connected with alternate openings of the outer row by long narrow portions, conductors substantially filling the conductor receiving openings, end rings of small crosssectional area integral with the conductors in the outer row of openings forming a high resistance, low reactance squirrel cage winding, and end rings of large cross-sectional area integral with the conductors in the 1nncr row of openings forming a low resistancc, high reactance squirrel cage winding.

2. In an induction motor, a rotor having inner and outer rows of openings, adjacent openings of the inner row being connected by long narrow portions with alternate openings of the outer row whereby alternate deep and shallow slots are formed, conductors substantially filling said slots, end rings of small cross-sectional area integral with the conductors in the shallow slots and with the outer portions of the conductors in the deep slots forming a high resistance, low reactance squirrel cage winding, and end rings of large cross-sectional area integral with the inner Portions of the conductors in the deep slots orming a low resistance, high reactance squirrel cage winding.

3. In an induction motor, a rotor having an inner and an outer row of openings, the openings in the outer row being greater in number than the o enings in the inner row and each opening 0? the inner row'being connected with an opening in ,the outer row by a narrow portion, conductors in said openings, end rings of relatively high resistance cast integral with the conductors of the outer row and end rings of relatively low resistance cast integral with the conductorsof the inner row.

4. In an induction motor, a rotor having a circumferential row of inner openings, each opening having a long narrow portion extending radially outward therefrom, and having outer openings arranged near the periphery and arranged radially opposite the spaces between the inner openings, conductors in said openings, end rings of relatively low resistance connecting the ends of the conductors in the inner openings and end rings of relatively high resistance connecting the ends of the conductors in the outer openings.

5. An induction motor comprising a stator and a rotor, said rotor having a plurality of conductor receiving openings each and all electrically communicating with the periphery, and having a squirrel cage winding comprising conductors in said openings having respectively a relatively low reactance, a relatively high reactance and an intermediate value of reactance, a pair of end rings connecting together the conductors having the relatively low and the intermediate value of reactance, and a pair of end rings connecting together the conductors having the relatively high reactance.

In witness whereof, I have hereunto set my hand this 26th day of November, 1924.

SVEN R. BERGMAN. 

